There is current interest in oil and mineral exploration on the continental shelf. The evidence suggests that there are vast untapped reserves of oil under many continental shelf regions, for example off the coast of Mexico.
There are several logistical problems attendant to the development of offshore petroleum reserves. Once the oil has been drilled, the immediate problem is getting the oil to shore, where it can be used. Loading oil from the drillsite directly into tankers is one solution. This would involve intermittent shut down of petroleum extraction when the storage tanks at the drilling facility become filled to capacity; also the hazard of ship-to-facility collisions could interrupt operation. Moreover, for high volume operations, it is advantageous to operate continuously. For this reason, it is desirable to pump the oil initially into a large volume storage facility where it can be safely held for later transfer into supertankers.
A large volume storage facility would be desirable for offshore petroleum exploration. By allowing for continuous drilling operations it would obviate shipping scheduling problems. A storage facility also would hold and protect the oil during periods of hurricanes or heavy weather, when transfer of oil onto ships would be hazardous. Finally, a storage facility can provide usable above-water space for a wide variety of purposes, functioning in effect as a parcel of real estate in marine environment.
Constructing and deploying a large volume storage structure is difficult. The lack of available real estate in the ocean and the dynamic nature of the ocean environment makes it imperative that such a structure be prefabricated on land and towed out to sea. One major problem in constructing a large volume floating structure is to assure sufficient draft along the waterway to permit towing of the structure to the installation site. Many proposed oil exploration areas have good, flat, sandy bottoms, but at depths of up to about 65 feet. Seasonal hurricane or other storm waves make it desirable to maintain a deck height above water of at least 25 feet. Thus a major problem is one of building structures which are towable yet which have a 25 foot deck height for sites which may be on the order of 60 feet deep.
While it is possible to construct a single 90 foot high facility, the draft of such a structure limits the building sites to those with sufficient deepwater access. In this regard, there are few dredged harbors which exceed even a 38 foot depth and natural harbors are generally more shallow. Hence, towing of a 90 foot high concrete structure offshore would necessitate deep dredging of any given harbor area. Such an approach would be prohibitively expensive.
Assuming, however, that an appropriate structure could be fabricated onshore and deployed offshore, there are additional problems. Due to its high cost, it is desirable that any structure be fabricated of materials which will not corrode or weather in a marine environment. Moreover, if the facility is to be used for storing large volumes of oil or other flammable liquids, it is imperative that the risk of fire or explosion be reduced to a minimum. Furthermore, the structure should be designed, if possible, to accommodate internal breakage or failure so as to minimize the risk of a large scale oil spill.
There is need for a large volume storage structure which can be built economically with a "towable" draft and having a "weatherproof" deck height for a moderately deep installation. The need extends to a structure which is self-contained, strong, durable, lightweight and which has a long useful life. Finally, the need extends to a procedure for deploying such a structure from an onshore fabrication site.